Performance of a solar air heater incorporating thermal storage

Lombaard, Francois (2002-12)

Thesis (MEng)--Stellenbosch University, 2002.

Thesis

ENGLISH ABSTRACT: In the present study, research was conducted to determine the feasibility of water energy storage through which the output of heated air by an upward facing solar air heater could be prolonged. Following a systematic approach, a number of experimental test swere initially performed on an upward facing solar air heater in order to obtain a benchmark that could be used to evaluate the influence of water storage during the day-time performance of a solar air heater. As expected, an increase in the air mass flow rate not only led to an increase in the collector efficiency but also to a decrease in the temperature gain across the collector. In addition, a number of day- and night-time experiments were executed on a plastic covered water tank in order to evaluate it's ability to store and discharge thermal energy. Results clearly indicated that the plastic covered water tank was both an ideal collector and storage medium of solar energy. Experimental results also revealed that the plastic covered water tank was an ideal source of thermal energy for a solar air heater during night-time operation. Subsequently, both day- and night-time experiments were performed on an upward facing solar air heater in which plastic covered water tanks were installed. Day-time experimental results revealed that the modified solar air heater still had the same collector efficiency tendency, as observed in the initial solar air heater experiments, but that the water energy storage led to a dramatic decrease in the absorber plate temperature and in the corresponding temperature gain experienced across the collector. In contrast, the night-time operation results clearly indicated that the water energy storage was not only able to prolong the output of heated air by the solar air heater, but was further able to increase the air temperature by between 7.5 and 1.5 °e, depending on the air mass flow rate. It was furthermore shown in the study that available theory is able to accurately predict the performance of an upward facing solar air heater, either with or without water energy storage, as long as the equations are employed within their range of validity

AFRIKAANSE OPSOMMING:In die hierdie studie is daar ondersoek ingestel na die lewensvatbaarhied van son-energiestoring in water ten einde die tydperk van lugverhitting deur 'n son-Iugverwarmer te verleng. 'n Sistematiese prasedure is gevolg waardeur daar aanvanklik 'n aantal eksperimente op 'n son-Iugverwarmer uitgevoer is am sodoende die eienskappe van so 'n lugverhiUingstelsel, sander energie storing, te vekry. Die resultate het getoon dat 'n toename in die massavloei tempo van die lug lei tot 'n toename in die kollektor effektiwiteit van die stelsel, maar terselfdetyd lei tot 'n afname in die temperatuur styging in die kollektor. Met die eienskappe van die lugverwarmingstelsel bekend, is daar voorts 'n aantal dag- en nag-eksperimente uitgevoer op 'n plastiek bedekte watertenk am die storing en vryselling van termiese energie deur die watertenk te kwantifiseer. Die resultate het daarap gedui dat die plastiek bedekte watertenk nie net beide 'n goeie kollektor en stoor medium vir son-energie is nie, maar oak dat dit 'n ideale bran van termiese energie vir 'n lugverwarmingstelsel tydens die nag is. Met inagname van die vorige resultate, is daar dan 'n aantal plastiek bedekte watertenks in die apparaat geinstalleer, en 'n aantal dag- en nag-eksperimente is uitgevoer. Die dageksperimente het getoon dat die die nuwe lugverwarmer met water energie storing dieselfde eienskappe toon ten opsigte van die kollektor effektiwiteit as die oorspronkilke son-Iugverwarmer. Tog, as gevolg van die laer absoberende plaat temperature was die temperatuur toename in die kollektor heelwat laer. In kontras hiermee dui die nagresultate aan dat die plastiek bedekte watertenks nie net die vermoe het am die tydperk van lugverwarming te verleng nie, maar oak dat die lug tempertuur, afhangende van die massavloei tempo van die lug, met tussen 1.5 en 7.5 °C verhoog kan word. Die studie het laastens oak getoon dat dit moontlik is am met behulp van beskikbare teorie die temperatuur toename in die kollektor van 'n son-Iugverwarmer met of sander water energie storing, akkuraat te voorspel, mits die vergelykings binne hul geldige gebiede gebruik word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/52993
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